Vanillin purification



VANILLIN PURIFICATION 2 Sheets-Sheet 1 lled Oct. 17, 1958 ATTORNEYATTORNEY d Patented Aug. i4, i962 3,fi,566 VANlLLlN PUREHCATEN Eugene W.Schoeffel, Kronenwetter, Wis., assigner, by mesne assignments, toAmerican Can Company, New York, NX., a corporation of New Jersey FiledOct. 17, 1958, Ser. No. 767,959 2 Claims. tl. Zeit-6%) The presentinvention relates to the puriiication of vanillin and more particularlyrelates to a process for continuously purifying crude vanillin toachieve pure, crystalline white vanillin and recover separately some ofthe compounds present as impurities in the crude vart'lliu.

While natural vanillin is extracted from the vanilla ..bean, severalmethods are known for the chemical preparation of vanillin. One suchmethod involves a chemical reaction Vwith guaiacol, a relativelyexpensive derivative of coal tar. Another method involved the partialoxidation of lignin in an alkalinized waste sulte liquor. Because of thefavorable economic factors involved, the partial oxidation 'of Wastesuliite liquor has generally been the most widely used chemical 4sourceof vanillin. However, only about 9 percent of the Waste sulte liquor isconverted to vanillin, the remainder being impurities wluch must beeliminated.

The `aforementioned methods have produced a crude vanillin, having manyimpurities therein that render the product unsuitable where high purityis required. Pure vanillin has a melting range of S2-83-5 degreescentigrade, white crystalline appearance, produces colorless solutions,and is colorless in the liquid state. Crude vanillins contain impuritiesthat lower the melting point, produce colored solutions, and color theliquid state. These impurities are compounds containing phenolic andcarbonyl groups with solubilities similar to vanillin. The three mainimpurities present in crude vanillin obtained from guaiacol areisovanillin, guaiacol and orthovanillin. A crude vanillin distillateobtained from lignin contains yabout 90 percent vanillin and about l0percent impurities and has a melting range of 62-78 degrees centigrade.The characteristics of a particular crude vanillin depend on the ratioand composition of the impurities and the moisture content. The mainimpurities of crude vanillin derived from lignin are S-formylvanillin,para-hydroxybenzaldehyde and acetovanillone. Other impurities such asdehydro-di-vanillin, S-carboxyvanillin and oxystilbene are present tosome extent but have been largely removed by the routine purificationand extraction procedures during the prior production of the crudevanillin from lignin.

The present invention resides in the concept of a process for purifyingcrude vanillin by dissolving crude vanillin in a solvent mixture ofVWater and 40 to 60 percent by weight of methanol, preferably 40 percentby weightmethanol; crystallizing vanillin-containing solid from thesolution; dissolving the vanillin-containing solid in a solvent mixtureof water and 40 to 60 percent by weight methanol, preferably G percentby weight methanol; crystalhzing from the solution pure white vanillinhaving a melting range of 8283.5 degrees centrigrade; separatingmethanol and4 recycling the separated methanol to form the vanillinsolutions; and separating vanillin and other compounds from thefiltrates, whereby a continuous process is achieved for producing a highyield of pure vanillin and selectively isolating impurity compoundspresent in ythe crude vanillin.

Throughout the specification, the term percent alone means percent Vbyweight.

A physical embodiment of the invention is illustrated in the`accompanying drawing showing a ilow sheet of the purification accordingto the invention of crude vanillin derived from lgnin. Following is ageneral description of the embodiment of the invention illustrated inthe accompanying drawing.

Crude vanillin distillate containing about -90 percent vanillin andderived from the partial oxidation of lignin in suliite waste liquor isdissolved in a solvent mixture of 40 percent methanol and 6) percentwater.

The solution is cooled with the resulant precipitation of a somewhatpurified vanillin-containing solid having a melting range of 82-83degrees centigrade. The solid is filtered and dissolved in a solventmixture of 50 percent methanol and 50 percent water. The solution iscooled with the precipitation of crystalline, white vanillin melting at82-83.5 degrees centigrade. The vanillin is filtered and dried. lf awater crystallization is desired, the vanillin is dissolved in hot waterand the solution cooled to produce a water crystallized vanillin. Thevanillin is centrifuged from the mother liquor and dried.

The iiltrate of the rst crystallization is distilled to remove methanolthat is recycled to form the rst solution of crude vanillin. The residueremaining afterdistillation is thereafter selectively treated toseparate 5-formylvanillin, vanillin, `and para-hydroxy-benzaldehyde. Theimpurities can be separated by treating the residue with zinc `acetatesolution, zinc sulfate solution, magnesium carbonate or magnesium oxide.Preferably, as in the illustrated embodiment of the invention, theimpurities are selectively separated as substantially pure compounds bythe following procedure.

The residue is treated with magnesium carbonate with the resultantprecipitation of magnesium S-formylvanillinate, which is filtered. Thefiltered precipitate is moistened with aqueous 50 percent sulfuric acidand thereafter extracted with ethylene dichloride. The ethylenedichloride solution is distilled -to remove ethylene dichloride andproduce substantially pure 5-formylvanillin.

The filtrate remaining after removal of magnesium 5- forrnylvanillinateis treated with magnesium oxide with the resultant precipitation ofmagnesium vanillinate Ithat is filtered. Aqueous 50 percent sulfuricacid is added to the magnesium vanillinate precipitate and the vanillinextracted with butanol. The vanillin is recovered from the butanolsolution.

The filtrate remaining after removal of magnesium vanillinate isaciditled, concentrated, and extracted with hot ethylene dichloride toremove .the para-hydroxyhenzaldehyde. The ethylene dichloride solutionis separated from the aqueous layer and cooled to precipitatepara-hydroxybenzaldehyde. The mother liquor contains the acetovanillone.

There now follows a specific description of the physical embodiment ofthe invention illustrated in the accompanying drawing.

-Fit a 5 liter 3-necked flask with a thermometer, stirrer and condenser.Add to the flask 1450 grams of crude vanillin derived from lignin and1170 cubic centimeters of a solvent mixture of 60 methanol. Stir andwarm the `contents through the temperature range of 30-60 degreescentigrade to dissolve the crude vanillin in the solvent mixture. Afterall the vanillin dissolves, `cool the contents of the ask rapidly to23e25 degrees centigrade. Seed the solution lwith one gram ofcrystalline vanillin obtained from the end product of this process.Continue stirring the solution. Crystals soon appear and the temperaturerises slightly. Maintain the temperature of the mixture within i2centignade degrees of the initial crystallization temperature for onehour. Thereafter, while stirring steadily, slowly cool the contents ofthe ilask over ya period of about three hours to reach a temperature ofabout 5 degrees centigrade at the end of the three hour period. Maintainthe mixture at 5 degrees centigrade for an `additional two hours.

percent water and 40 percent Filter the crystalline mass. Wash the solidlter cake with four successive portions each of 250 cubic centimeters ofwater having a temperature of 0-5 degrees centigrade. Continue .to drawair through the lter funnel until the solid is substantially air dry.The dry solid weighs 1110 grams i2() grams and melts at Sp1-S2 degrecscentigrade.Y Combine the tiltrate `and washings.

' Determine the dry vanillin and moisture content of the solid ltercakebyweighing a portion of the cake, drying it at about 60 degreescentigrade for three days, weighing the dried portion, and computing themoisture content and the vanillin content. Knowing the vanillin andmoisture vcontent of the solid ltercake, prepare a mixture of methanoland water that, when combined with the 1110 gram solid, will producelll() cubic centimeters of a mixture of exactly 50 percent methanol and50 percent water in which the solid will dissolve.

i Add the prepared mixture of methanol and water to the previously used5 liter 3-necked flask fitted with a thermometer, stirrer and condenser.Add the 111() gram solid lter cake to the flask. Warm the mixture, whilestirring, to 40-50 degrees centigrade to produce a slightly coloredsolution. Thereafter, the solution is rapidly cooled to about 35 degreescentigrade. Then seed the solution with l gram of finished purevanillin. Next, While stirring constantly, slowly cool the mixture forone hour to 32 degrees centigrade. Crystallization begins and thetemperatureV starts to rise. Maintain the mixture at a temperaturelbetween about 30-34 degrees centigrade for one hour. Thereafter, whilestirring, slowly cool the mixture over a period of two hours to reach atemperature of 13 degrees centigrade. Filter the crystalline solid. Washthe solid with four portions of 250'cubic centimeters of water at atemperature of O-l3 degrees centigrade. Suck air through the filterfunnel to substantially air dry the solid. Dry the solid to produce1090:*20 grams of pure, white crystalline vanillin, melting at 82- 83.5degrees centigrade. This vanillin is colorless in the liquid state andforms a colorless solution.

Combine the wash -water from the rst washof the preceding paragraph,containing most of the methanol,` with the iiltrate.` Return thecombination to the ,crudeY vanillin and employ it as part of the aqueous40 percent methanol solvent mixture. Return the second, third, andfourth Wash waters to the rst crystallization and employ them as washwaters for the iirst solid precipitate.

The recovered liquids from the second crystallization have the followingcomposition: l

In order to produce a water crystallized vanillin, distained at about 90degrees centigrade that the concentrationV of the resulting solution isabout 45 grams of vanillin per liter of solution. Next, cool thesolution until crystallization beginsat about50 degrees centigrade.Maintain the temperature at about 45 degrees centigrade for two hours.Then slowly cool the mixture to reach a temperature of 13 degreescentigrade in three hours.

tigrade for one hour to complete crystallization. Filter the crystalsthrough a lter funnel. Suck air through the solid iilter cake tosubstantially air dry the crystals. Then Vsolve the crystalline vanillinin suicient hot water main- Next, maintain the temperature at about 13degrees cen- Y separation of the methanol,

para-hydroxybenzaldehyde. lA residue resulting from f completely dry thecrystals to produce pure white crys- Y iltrate to the waste sulte liquoroxidation plant for useV in making bisultiting solution and variousdiluents employedinthe process. Y

The combined ltrate and washings from the rst alcohol crystallizationcontainV methanol whichY can be separatedand used in the formation ofthe solutions of Y vanillin in aqueous methanol. The combined filtrateand washings also contains the following dissolved solids: 60-70 percentvanillin, 25-35 percent para-hydroxybenzaldehyde, 6-9 percent5-formylvanillin, and 4 6 percent acetovanillone. The followingprocedures effectuate the 5-formylvanillin, vanillin and followingprocedures contains the bulk of the acetovanillone. Y v Y The combinedfiltrate and washings from the iirst crystallization has a volume of2100 cubicV centimeters and contains:

210i20 grams vanillin Y Y 9115 grams para-hydroxybenzaldehyde ZOiS grams5-formylvanillin 131-3 grams acetovanillone 430+ cubic centimetersmethanol aqueous methanol.

To theA residue from ythe distillation, add 8.0 grams of Y magnesiumcarbonate for each liter of residue solution. Stir the mixture whilemaintaining the temperature at 50-60 degrees centigrade for about lhour. A precipitate n of magnesium 5-formylvanillinate forms that is ane powder that is diicult to filter and centigrade. For tiltratlon, itrequires a lilter cloth Ywith pores in excess of 400 mesh to produce aclear separation. A 720 mesh.

stainless steel cloth gives a clear separation immediately Whereas 400mesh cloth permits some of the precipitate to pass through the iilter atthe start of the ltr'ation.v

The u se of a high speed centrifuge is advantageous.

While keeping the mixture hot, lter it under a pressure of 30 pounds persquare inch guage through a 2 inch v diameter lter made of 720 meshstainless steel cloth.

The ltration is completed in 1-2 hours.'V Wash the ltered precipitatewith two 50 cubic centimeter portions of methanol maintained at about5() degrees centigrade. Combine the filtrate and washings and separate.vanillin therefrom as outlined below. Y Y Y Place the damp solidmagnesium 5-formylvanillinate`v i in a ask equipped with a mechanicalstirrer and a thermometer. Add 17.5 grams of aqueous 50 percent sulfuricacid and 25 cubic centimeters of ethylene dichloride. Warm the mixtureto 70-80 degrees centigrade and stir. The magnesium'sulfate produceddissolves in the water IayenandS-formylvanillin dissolves in theethylenedichloride layer. Separate the ethylene dichloride layer,VExtract the aqueous layer with from the aqueous layer. another 25 cubiccentimeter portion of hot ethylene dichloride. Combine the ethylenedichloride extracts and wash them with two 5 cubic centimeter portionsof Water at 60--80 degrees centigrade.

Combine the water washes with the aqueous layer and steam distill thecombination to remove ethylene dichloride. Return the separated ethylenedichloride tothe extraction of the 5-formylvanillin. The aqueous residuefrom the steam distillation, containing the' water-soluble magnesiumVsulfate and less than 5 grams per liter of aldehyde computed asvanillin, is vented to the sewer.

Place the combined ethylene dichloride extracts in a distillationcolumn. Distill the ethylene dichloride oit under atmospheric pressure.Place the residue in a Vacuum distillation apparatus equipped with anoil bath. At a reduced pressure of 2 millimeters of mercury, distill theS-formylvanllin at 173-175 degrees centigrade using an oil bathtemperature of 168-189 degrees centigrade. Pure 5-formylvanillin isobtained.

Now the combined ltrate and washings from the crystallization ofmagnesium 5-formylvanillinate are treated to separate vanillintherefrom. Warm the combined filtrate and washings to 50-60 degreescentigrade while stirring. Add about 26 grams of magnesium oxide foreach liter of combined iiltrate and Washings. Employ commercial grade ofmagnesium oxide that assays about 90.8 percent magnesium oxide. Themagnesium oxide dissolves temporarily and a temperature increase of 3-8centigrade degrees occurs. In less than 60 seconds after the solutionforms, magnesium vanillinate precipitates copously from the solution.Stir the mixture for l hour at 50-60 degrees centigrade. Filter thesolid precipitate over a 100 mesh stainless steel cloth under a pressureof less than pounds square inch gauge. Wash the precipitate cake withthree 87 cubic centimeter portions of hot water at 80-90 degreescentigrade. Combine the wash waters with the filtrate and transfer tothe para-hydroxybenzaldehyde recovery system described below.

Place the damp magnesium vanillinate, weighing about 200 grams dry, in aask fitted with a thermometer and stirrer. Add hot aqueous 50 percentsulfuric acid at a temperature of 80-90 degrees centigrade. Add 100cubic centimeters of hot water and an excess of butanol. Stir themixture while maintaining it at 80-90 degrees until the vanillindissolves in the butanol phase. Separate the butanol phase. Extract thevanillin from the butanol phase with an aqueous solution of percentsodium biy sulte. Separate the aqueous -bisultite phase from the butanolphase. Add sulfuric acid to the aqueous phase to decompose the vanillinbisuliite. Extract the vanillin from the aqueous phase by mixing withhot butanol. Hot ethylene dichloride can also be used as the extractant.Separate the hot butanol phase from the aqueous phase. Add calciumcarbonate to the butanol solution to elect neutralization. Next, filterthe mixture to separate any solid material. Distill the filtrate toremove butanol solvent. Steam distillation can also be employed. Placethe residue remaining after removal of the butanol solvent in a vacuumdistillation apparatus. Vacuum distill the residue to produce Ivanillinhaving the following composition:

97 percent vanillin;

Less than 2 percent para-hydroxybenzaldehyde; Less than 1 percent5-formylvanillin;

Less than 1 percent acetovanillone;

Less than 0.1 percent other impurities.

This vanillin fraction is returned to the alkaline bisulte stage of theprior sulte liquor oxidation plant in Vorder to effectuate removal ofthe acetovanillone.

The combined filtrate and washings from the filtration of thecrystallized magnesium vanillinate has the following approximatecomposition:

Less than 10 grams vanillin per liter of solution;

Less than 5 0-75 grams para-hydroxybenzaldehyde per liter of solution;

Less than 5 grams of 5-forn1ylvanillin per liter of solution;

Less than 7 grams of acetovanillonerper liter of solution;

About 90 grams of total aldehyde computed as vanillin per liter -ofsolution;

30-35 percent by volume of methanol.

This combined ltrate and washings is treated to removepara-hydroxybenzaldehyde therefrom by the following hyde per liter ofthe procedure. Neutralizethe combined filtrate and washings by addingaqueous 50 percent sulfuric acid until a pH of 4.5-5.0 is achieved.Fractionally distill the acidied solution to remove a fractioncontaining -10() percent methanol. Recycle the methanol fraction to formthe solvent for the crude vanillin. After the removal ofthe methanolfraction; further distill to concentrate the residue to a volume ofabout 160 cubic centimeters. Thereafter, extract the aqueous residuewith two 50 cubic centimeter portions of hot ethylene dichloride at atemperature of 60-70 degrees centigrade. Separate the aqueous layer fromthe ethylene dichloride layer.

Steam distill the separated aqueous layer to recover ethylenedichloride. Recycle the recovered ethylene dichloride to the previousethylene dichloride extraction step. The aqueous residue remaining aftersteam distillation contains the bulk of the acetovanillone.

Permit the hot ethylene dichloride extract to settle to separate thewater. Separate the settled water layer. Next, cool the ethylenedichloride extract to 10-13 degrees centigrade while stirring. Aprecipitate forms.- Filter the precipitate over a iilter maintained at atemperature of lG-l3 degrees centigrade. Wash the precipitate with two25 cubic centimeter portions of ethylene dichloride at 10-13 degreescentigrade. Add these washes to the ltrate. Distill the combined washesand filtrate to remove ethylene dichloride that is returned to theprevious ethylene dichloride extraction of para-hydroxybenzaldehyde.Recycle the residue remaining after distillation to the vanillinalkaline liquor 'charge of the prior Waste sulte liquor oxidation plant.

Dissolve the solid precipitate in water until a concentration of -150grams of para-hydroxybenzaldehyde per liter of solution is obtained.Steam distill the solution at atmospheric pressure to remove ethylenedichloride. Recycle the removed ethylene dichloride to the priorextraction step. Treat the aqueous solution with 2 grams per liter ofcharcoal and filter to remove solid. Cool the aqueous filtrate to 10-13degrees centigrade, while stirring, with the resultant precipitation ofcrystalline para-hydroxybenzaldehyde. Filterthe precipitate at 10-13degrees centgrado. Wash the precipitate with six portions of -water atabout 13 degrees centigrade, each water wash portion being 5 percent byvolume of the ltrate. obtain a yield of 38-60 grams ofpara-hydroxybenzaldecombined ltrate and washings from thecrystallization of magnesium vanillinate. The dry product assays to havea content of 98-100 percent parahydroxybenzaldehyde.

Combine the filtrate and six water washings yof the previous paragraphand return them to the vanillin alkaline liquor charge of the priorwaste sulfite liquor oxidation plant. Or, the combined ltrate and waterwashings can be recycled to the distillation column where the methanolis removed from the magnesium vanillinate filtrate.

It is thus seen that the invention provides a process for continuouslypurifying crude vanillin to produce pure, white crystalline vanillin andselectively isolate several mpurities present in crude vanillin derivedfrom lignin.

While the invention has been illustrated with a physical embodiment, itsscope is limited only by the subjoined claims.

I claim:

l. A process for purifying crude vanillin comprising the steps:dissolving said crude vanillin in an aqueous methanol solvent containingfrom about 40 to about 60 percent of methanol to form a solution;cooling said solution to form a precipitate; filtering the precipitate;dissolving said precipitate in an aqueous methanol solvent containingfrom about 40 to about 60 percent methanol to form a second solution;cooling said second solution to form a second precipitate; and,filtering said second precipitate to isolate pure vanillin having amelting range of 82 to 83.5 degrees centigrade.

Dry the precipitate toprecipitate to isolate pure vanillin having amelting range l 421.V A process for purifying crude vanillin comprisingthe References Cited in the le of this patent steps dissolving saidcrude'vanil'lin inra solvent mixture Y Y s UNITED STATES PATENTS fjabout40 percent methanol and about 60 percent Water 1 954 766 Fisch'es Apr10k 4 T to form a solution; cooling said solution to forma precipi-`2069185 Hibbert e'"" Jan: .26 1937A tate; filtering the precipitate;dissolving said precipitate in 5 Y 2187366 Schulz Iam 1'6 1940 a solventmix-ture of about' -50 percent methanol and about A506;540 Y Bryan May2, 1950 5.0 percent of Water to form a second solution; cooling said Y*OTHER REFERENCES v `second solution to form a precipitate; and,lteringrsaid Y Y Weissbertger: Part l, Separationrand Purication, vol.

of to 83.5 degrees centigrade. O I V, 2nd ed. (1956), p.` 556.

1. A PROCESS FOR PURIFYILNG CRUDE VANILLIN COMPRISING THE STEPS:DISSOLVING SAID CRUDE VANILLIN IN AN AQUEOUS METHANOL SOLVENT CONTAININGFROM ABOUT 40 TO ABOUT 60 PERCENT OF METHANOL TO FORM A SOLUTION;COOLING SAID SOLUTION TO FORM A PRECIPITATE; FILTERING THE PRECIPITATE;DISSOLVING SAID PRECIPITATE IN AN AQUEOUS METHANOL SOLVENT CONTAINING